(CNN) -- A navigation error pushed NASA's latest Mars mission fatally close to the planet Thursday, leaving the $125 million probe lost in space and possibly destroyed.

Engineers had thought the Mars Climate Orbiter was approaching the red planet at the correct altitude before it fired its engine to slow itself down to 9,840 mph so gravity could pull the craft into orbit around Mars.

The engine fired properly but the spacecraft was hurtling along on a course that brought it too close to the planet's surface and deep into Mars' atmosphere.

"It potentially resulted in the loss of the mission," said Richard Cook, manager of the Mars Surveyor '98 program, which includes Climate Orbiter.

The probe came within 60 km (36 miles) of the planet -- about 100 km closer than planned and about 25 km (15 miles) beneath the level at which the spacecraft could survive, mission members said.

"We don't believe, on the spacecraft side, that it is survivable," said project manager John McNamee. "It looks like something was wrong with the ground navigation."

Artist's rendering of the Mars Climate Orbiter

The spacecraft may have crashed into the planet, but mission members said they were still looking into the situation and didn't know one way or the other.

The steering problem came as a result of bad computer commands sent to the spacecraft, a problem with the sending of commands or some other software problem, said Richard Cook, manager of the Mars Surveyor '98 program which includes Climate Orbiter.

Following a 286-day journey, the Mars Climate Orbiter engine ignited as expected at 5:01 EDT, but engineers waiting for a signal expected about 25 minutes later when the satellite cruised out from behind the planet heard nothing.

Engineers worked Thursday to recalculate the spacecraft's location so they could repoint gigantic radio antennae on Earth to receive signals from Climate Orbiter, but the prospects for finding the craft were dim.

Project scientist Richard Zurek likened the effort of searching for the spacecraft to "looking for a signal in the cosmic haystack."

The satellite was to map and photograph Mars' atmosphere and serve as a communications relay for two lander missions. The lander missions will go on and communicate with Earth in other ways, but the science mission probably is lost.

The spacecraft may have been heading the wrong way for days, McNamee said. Engineers last tweaked the spacecraft's course by firing thrusters on Climate Orbiter on September 15.

Mars Polar Lander

But it is difficult to know definitely where a probe is in space until it is close to another object. Wednesday, it looked like Climate Orbiter was coming in a bit lower than expected but there was no firm data to confirm exactly how low until it arrived at Mars Thursday, Cook said.

"When you get below a certain level you have concerns about overheating the spacecraft or potentially breaking pieces of it off," Cook said.

That could explain why ground stations received no signal from Climate Orbiter -- it may be incapable of sending one.

In the minutes when the first post-firing signal was to come in, engineers in the control room at NASA's Jet Propulsion Laboratory, shown on NASA-TV, were grim-faced as the minutes ticked by with no signal from Climate Orbiter.

Flight operations manager Sam Thurman alternated between staring at his monitor, staring at flight plans and pulling at his wedding band.

At 5:36 a.m., he looked at his watch and grimaced. Minutes later, engineers in the control room stood up and started making new plans.

NASA and Russian/Soviet missions to Mars have had mixed results over the years, with NASA scoring loads of data in the 1970s with the Viking landers and in 1997 with the Mars Pathfinder's novel airbag landing, robotic rover and spectacular color images.

However, NASA's big-budget Mars Observer was lost just before it arrived at Mars in 1993. Mars '96, a Russian mission for which NASA also had high hopes, was destroyed during a launch accident.

The Thursday morning events were critical to NASA's first effort to look directly for water on Mars and study its weather closely, with the spacecraft set to enter the red planet's orbit to ready itself for contact with two upcoming lander missions.

Engineers avoided the worst case scenario -- no engine firing. That would have allowed Climate Orbiter to hurtle past Mars into space.

But the alternative -- losing contact with the spacecraft or its destruction-- also will be mission stoppers, if confirmed.

However, a permanent loss of contact with Climate Orbiter would not stop the mission of its partner spacecraft -- Mars Polar Lander -- set to land on Mars on December 3, project scientist Richard Zurek said.

Climate Orbiter was to relay signals from the lander to Earth. Less data would be returned, but the same scientific questions can be addressed, said Carl Pilcher, a space science administrator at NASA Headquarters.

The lander could use its own radio transmitter to communicate with Earth if it had to, Pilcher said. Also, Mars Global Surveyor, a NASA spacecraft currently mapping the planet, also could relay the lander's signals.